The present invention relates to a suspension device for vehicles, especially for railborne high-speed vehicles, which is arranged between the passenger car and the chassis and which has at least one flexible spring with low oscillation frequency, as well as a damping element connected in parallel to this spring.
Up to now, the suspension devices with spring action used for passenger cars in railroad and magnetic track systems have usually been purely passive. When the traffic systems attain higher speed ranges higher, demands are made on the spring action of the suspension device. If a passive suspension system is used, these demands can only be met, to the detriment of the passengers' comfort.
To decouple the passenger car, as far as vibrations are concerned, from the irregularities of the tracks, the springs must be flexible. In order to prevent the passenger car from being subjected to too high acceleration rates, when during lateral wind the trains pass each other or when they emerge from a tunnel, the spring action should function, to the greatest degree possible, as a hard coupling.
Since, thereby, the characteristic curve of the spring must have a non-linear form (flexible in the working range, stiff in the end stop ranges), so that deflections are restricted, the result is that powerful disturbances cause high acceleration values to occur.
The reason for having a practical limit for flexible spring systems is that, when the car is subjected to load fluctuations, the more flexible the spring action is, the greater that the spring excursions become. Nevertheless, to be able to achieve spring systems with relatively low frequencies, these systems are provided with so-called level control systems. These level control systems convert the spring system into an active system, whereby, as a rule, in the case of every active spring element, the distance between the spring-mounted mass and the mass which is not equipped with springs is measured, and the spring element is re-adjusted as a factor of this distance. Thus, for example, in the case of active pneumatic springs, the quantity of air in the spring can be modified as a factor of the mentioned distance. Here, the stipulation is that after an adequate recovery time, a preselected nominal distance is set between the spring-mounted mass and the mass which is not equipped with springs.
The operational limits of this type of active spring system are quickly reached, when the oscillation frequency is relatively low, the positioning and resetting rate of the level control system is relatively low and the permissible spring excursion is small or limited, as well as when the load fluctuations, which affect the spring-mounted mass, for example, the car, and especially their time derivations are considered as large.
In order to increase travel comfort, the passenger car must have the lowest possible oscillation frequency. This can be realized, for example, by means of so-called flexible secondary spring systems. These types of secondary spring systems are arranged, for example, in the case of magnetically levitated vehicles, between the suspension chassis and the passenger car. Thereby, the travel of the spring systems must be as short as possible, in order to avoid, for example, rolling motions of the passenger car; on the other hand, the variations in the loads affecting the passenger car over time are relatively greater, especially when there is a lateral wind.
As measurements have shown, for example in the case of a magnetic-levitation transport system with a horizontal spring, which shows a non-linear spring characteristic curve, when travelling over turn outs rail points, acceleration values can appear on the passenger car of up to 2 m/s.sup.2 at a speed of up to 190 km/h. The high transverse acceleration, thereby, is a result of the passenger car overshooting into the stiff spring range. This disadvantage is even more noticeable, when trains pass each other, during a lateral wind, whereby acceleration values of up to 12.7 m/s.sup.2 can occur and the deflection can reach over 11 cm, with a static deflection of approximately 8.5 cm only.
An active spring element for high-speed railborne vehicles is known from German Published Patent Application No. 35 37 325. It is arranged between a mass, which is not equipped with springs, and a spring-mounted mass of the vehicle. It features a dynamic circuit consisting of a flexible spring with low oscillation frequency and an active actuator connected in series to this spring, whereby the active actuator serves to regulate the clearance level between the two masses to a nominal value. An active spring or damping element is provided parallel to this dynamic circuit. It has a damping or restoring characteristic, which is dependent on the spring excursion and is initially low and then, from the point of a critical spring excursion, becomes progressive in both directions.
The flexible spring can be a pneumatic spring, preferably with a linear spring characteristic curve, while the active actuator is a regulated, hydraulic final controlling element, whose length can be varied in the direction of the spring excursion. The active spring and damping element is an hydraulic power actuator, whereby one should not infer from this publication how this power actuator should now be controlled, to attain the desired effect.